No, the collector should connect to the LED. The transistor is “backwards” to the way one would usually use it; that’s the whole point — that’s how you get the avalanche behavior.
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I’m super confused. I have used this schematic and this transistor to make this circuit.
I swear it looks like the Emitter should go to the led.
Hello,
Do you have a Red LED you could try with? Blue LEDs have a higher forward voltage, so maybe that’s changing the way the circuit is supposed to work?
Just spit-ballin…
Cheers
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That’s the diagram I described as “wrong” in that writeup, although in fact it’s right if you’re viewing the transistor from the bottom (the end where the leads attach) — which I guess is a common way to show such leads. Anyway, definitely the collector to the LED. See Kerry Wong’s writeup
http://www.kerrywong.com/2014/03/19/bjt-in-reverse-avalanche-mode/
with this schematic
(which is for a slow, sub-audio LED blinking version, so ignore the big capacitor)
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It’s been a while since I made the circuit. I just don’t remember having any problems using that schematic. I know Ive used a few different transistors as well. One thing I remember is using bc558 oriented either way and still working. 
I’m not going to rely on that memory now obviously 
Just spit-ballin…
That is a very good point. The 2N3904 avalanches at around 9V and the forward voltage of a blue LED is around 3V (depending on current). So with a blue led you need more than 12V to get it to avalanche.
I’d just get rid of the LED, it isn’t needed for the circuit to function and removing it makes the circuit work at lower voltages.
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Hi! So if the transistor is right, what do you think might be the problem? I have read your article and seen that it is normal for this to just not work. Do you think there is anything else that has to be fixed, or it just won’t work?
Omitting the LED (connecting transistor collector directly to ground) is worth trying.
it didn’t work… but thank you for the suggestion!
anyway I don’t know what more to do, but maybe I will get another set of the same components and try it on breadboard this time
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While it may not be the issue this time, i have seen reports of this making a difference before.
@mtrovao lets double check which transistor you got.
it is the 2n3904 why? And I already did the bypass of the LED, connecting que transistor directly to the ground and it didn’t work too
I realize my advice is questionable at the moment, but the breadboard is always my first test before strip board. That being said I just spent all night taking a vco circuit from a working breadboard layout and putting it on stripboard only for it to not work. Spent hours troubleshooting to no avail. I scrapped it. I’m gonna order new parts and start again. Super frustrating. That’s how it is though. In this case to add insult to injury I have actually made a successful strip board of the circuit I failed on tonight. Best, for me anyway, was to scrap it. Start over fresh. You may have a faulty potentiometer. Had a few of those…
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Yep! Beginners mistake not to try breadboard first… Thank you for everything tho! Will get back here if I manage to make it work!
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Different transistors avalanche differently. In fact, not all of the same type will exhibit this behavior. You could try another of the same type and see if it works. Remember that this circuit is exploiting a behavior that isn’t normally ideal, so it may not happen for each one you try.
Also, while the name is “super simple” its simple only in terms of # of components. The success rate varies wildly for a lot of folks it seems.
Do not be discouraged, most diy stuff isnt this fiddly.
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recently tried this project, but as many of we, didn’t work, reading this thread I’m gonna try again tonight, so I’m posting my result after that,
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